FS two T5 HO ballasts vented passively cooled wil handle two 36" T5 bulbs each

[RuGlu6]

Originally Posted by milou

I have 4 x 39 w T5 HO and need to add 2 more T5 to make it 6 bulb. what do I need?

Ok i see what you mean now by retrofit.
yes if you want to add two more bulbs you will need a room for two more bulbs in the fixture and a ballast that will drive these extra bulbs.
or
If you have a canopy then you will also need a reflector or individual reflectors in addition to the extra ballast and bulbs.
hth